In machine elements having ball bearing articulations, where the bearing races do not move through a full rotation, it is a common occurrence that these bearings fail prematurely. A typical cause for these failures is a lack of lubrication, inducing excessive wear on the bearing parts.
In a bearing which is limited to an angular reciprocal movement, whether the bearing is greased for life and sealed, or grease packed manually upon installation, the lubricant is gradually displaced towards the low pressure region therein, such that the balls under pressure are deprived of lubrication. This condition results in an accumulation of abrasive substances, like metal particles from wear of the parts, in the high pressure region of the bearing races. It is a common occurrence also that the unlubricated portion of the bearing starts to rust, adding to the deterioration of the high pressure region.
The ensuing friction generates more abrasive particles from metal grinding, and heavier loading of the bearing due to obstructed movements of the balls. At this stage, the bearing generally deteriorates at an accelerated pace.
As a first example of an application where the bearings have a limited rotation, the support members of a gliding-style rocking chair swing back and forth in an angular movement. The bearings of those articulations also rotate back and forth in an angular movement, without moving around a full turn. The lubricant in those bearings is not circulated around the bearing races. Hence accelerated wear occurs, causing a premature squealing and cracking of the chair.
Similarly, articulated jib booms of industrial manipulators have pivots which are limited to an angular movement. The weight of the load being carried by the boom is always applied on the same balls of the bearings, and in the same region of the bearing races. Hence accelerated wear of these bearings results in a shaky motion of the boom caused by flat spots on some balls or rough regions in the bearing races.
In a further application and for similar reasons, the ball bearing articulations of a robotic arm must be maintained frequently in order to prevent wear of the bearings and a following loss of precision in that machine's movements.
With respect to this common problem with ball bearings, the inventor of the present invention is unaware of any device in the prior art to prolong the life of a ball bearing moving in a back and forth angular movement.